1. Field of the Invention
The invention relates to imaging devices which extract image information for three colors at a single imaging area.
2. Description Relative to the Prior Art
It is well known to convert a color image to electrical signal form using photoelectric apparatus which extracts image information for at least three basic colors. If solid-state imaging apparatus, such as a CCD imaging array, is to be employed for extracting such information, the number of elemental sampling areas on the individual array (or arrays) influences both array cost and availability. Indeed, the present state of the art allows for, in a single solidstate array, little more than sufficient elements to permit high quality monochrome imaging. Accordingly, if such color imaging is to be performed at a single area (i.e., on a single array), as is desirable for reasons of economy and to avoid relative color registration problems, a limited number of available elements must be allocated among all three basic colors. It is therefore important to use the available elements as effectively as is possible.
In U.S. Patent Application No. 555,477 to Bayer, filed March 5, 1975, now U.S. Pat. No. 3,971,065, patterned arrays of photosensitive elements are described which extract color image information in a highly efficient manner considering human visual acuity for color detail. According to Bayer the elements most closely corresponding to luminance response (for example green for a preselected green-red-blue basic color system) comprise substantially 50 percent of the array and are located along alternate diagonals of the array. This arrangement results in high spatial frequency sampling for luminance, the spectral component for which the human visual system has the greatest resolving power. Information regarding the other two colors is derived at respective ones of the remaining element locations. In the preferred implementation for such arrays, highly efficient sampling of the other two colors is achieved by intermixing elements for those colors with luminance-responsive elements on an alternative row basis e.g., green alternates with blue in one line and alternates with red on the next line and so on. A problem arises however when interlaced scanning is employed with such arrays in that a serious field-to-field color flicker occurs. In fact, this effect is so disturbing as to make it impossible to continue viewing the image reproducible from the derived color signals for any significant period of time.
One possible approach for overcoming the element allocation problems introduced by an interlaced scan is described in U.S. Published Patent Application B502,289. This approach, however, requires a special solid state imaging array which provides for overlapping of elements from one field to the other. Also, a rather elaborate filter configuration is required which associates with each zone (elemental area) of the array two or more sub-areas that have different light attenuation characteristics.